Valve clearance has a tendency to tighten up as the valves sink into the head a little from normal wear. I'm not as concerned with a "stuck" valve as I am with one that's lost enough clearance that it's staying slightly open instead of getting seated properly. The only way a valve cools itself is by transferring heat to the cylinder head through the valve seat every time it closes. If you haven't been adjusting the valves every time you do a tune-up, you might have a burned valve, not a stuck one. Hydraulic valve lifters have made us lazy over the past few decades. These old mechanical lifter engines need more TLC than one with hydraulics..
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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